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Modeling biomass flows at the farm level: A discussion support tool for farmers

Andrieu N., Nogueira D.M.. 2010. Agronomy for Sustainable Development, 30 (2) : p. 505-513.

DOI: 10.1051/agro/2009047

Many simulation models that are used to assess the impact of mixed farming systems have a high level of complexity that is not suitable for teaching farmers about the impacts of their practices. In this paper, we present a model that was developed and used with farmers as a discussion support tool to address the impacts of farming management strategies on farm resources. We assumed that the characterization of biomass flows at the farm level would provide a simple framework for designing a discussion support tool for farmers. The study was carried out in the semi-arid region of Brazil, where areas of native vegetation of the Caatinga Biome have been reduced in recent decades due to population pressure. In this region, simulation models are not used to discuss the impact of practices. We decided that a model for this purpose should: (1) be simple enough to be used by farmers, (2) be consistent with existing data, and (3) take into account the three main biomass management strategies. The model we built simulates biomass exports (harvest, animal intake, clearing vegetation of Caatinga), imports (purchase of fodder), and returns (animal manure) for farms with different vegetation types (Cenchrus ciliaris, Sorghum bicolour, Opuntia sp. and Caatinga native vegetation). We used the model to compare three management strategies over a 15-year period and found that the strategy that allows for the preservation of Caatinga vegetation is less sensitive to bad years but results in a reduced herd size.We validated the use of this model by testing it with farmers. We found that farmers were interested in using the model as a learning (38%), management (33%), or prospective tool (24%). This study shows that the dynamic modeling of biomass flows provides a simple and operational framework to analyze the impact of farming systems on farm resources with farmers. Contrary to current dynamic biophysical models that are based on extensive experimental data, this model does not give accurate predictions but allows both farmers and researchers to learn the impacts of farming systems. The complexity of the model should be increased progressively as farmers improve their understanding of the underlying processes.

Mots-clés : biomasse; modèle mathématique; brésil

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